JWST Detects Oldest Known Supernova — Light From a Star That Exploded 730 Million Years After the Big Bang

The James Webb Space Telescope has captured light from the oldest supernova yet observed: an exploding star that died when the universe was about 730 million years old, roughly 5% of its current age. The event, now cataloged as GRB 250314A, offers a remarkable glimpse into how the first massive stars ended their lives.

Why This Discovery Matters

Surprising similarity: Despite forming in an early, metal-poor universe, the blast resembles modern core-collapse supernovae. That was unexpected because the first generations of stars — made almost entirely of hydrogen and helium and often much more massive than today’s stars — might have produced different explosive signatures.

How It Was Found

In March, instruments recorded a 10-second flash of high-energy radiation known as a gamma-ray burst (GRB), a transient often associated with catastrophic stellar deaths. The Space-Based Multi-Band Astronomical Variable Objects Monitor (SVOM) detected the burst on March 14, triggering rapid follow-up observations worldwide.

NASA’s Neil Gehrels Swift Observatory refined the burst’s sky position. The Nordic Optical Telescope on La Palma indicated the source was extremely distant, and the European Southern Observatory’s Very Large Telescope measured a redshift consistent with an age of roughly 730 million years after the Big Bang.

Because cosmic expansion stretches light to longer (redder) wavelengths, astronomers predicted the supernova’s optical/infrared emission would peak several months after the initial gamma-ray flash. Webb observed that predicted brightening in July and confirmed the transient as a supernova. Webb’s infrared sensitivity was essential for detecting the stretched light and isolating the transient from the faint background.

Host Galaxy and Scientific Implications

The observatory also imaged the tiny galaxy that hosted the exploded star; in Webb’s images it appears as a faint red smudge. This diminutive system produced one of the earliest stellar deaths yet recorded and provides rare direct evidence of massive-star evolution in the universe’s first billion years.

Designation: GRB 250314A — Detected by SVOM on 14 March; brightening observed by JWST in July.

Overall, the finding suggests that at least some of the first massive stars ended their lives in explosions similar to those we observe in the modern universe, a clue that helps refine models of early star formation, feedback, and chemical enrichment.